Sleep modifies retinal ganglion cell responses in the normal rat

Recordings were obtained from the visual system of rats as they cycled norm ally between waking (W), slow-wave sleep (SWS), and rapid eye movement (REM ) sleep. Responses to flashes delivered by a light-emitting diode attached permanently to the skull were recorded through electrodes implanted on the cornea, in the chiasm, and on the cortex. The chiasm response reveals the t emporal order in which the activated ganglion cell population exits the eye ball; as reported, this triphasic event is invariably short in latency (5-1 0 ms) and around 300 ms in duration, called the histogram. Here we describe the differences in the histograms recorded during W, SWS, and REM, SWS his tograms are always larger than W histograms, and an REM histogram can resem ble either. In other words, the optic nerve response to a given stimulus is labile; its configuration depends on whether the rat is asleep or awake. W e link this physiological information with the anatomical fact that the bra in dorsal raphe region, which is known to have a sleep regulatory role, sen ds fibers to the rat retina and receives fibers from it. At the cortical el ectrode, the visual cortical response amplitudes also vary, being largest d uring SWS, This well known phenomenon often is explained by changes taking place at the thalamic level. However, in the rat, the labile cortical respo nse covaries with the labile optic nerve response, which suggests the corti cal response enhancement during SWS is determined more by what happens in t he retina than by what happens in the thalamus.